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Scan_Doc0095 - Notice that the percentages add up to 100.00...

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3.6 Percent Composition of Compounds 89 Forexample, forethanol, which hastheformula C 2 H s OH, themass ofeach element present and themolar mass areobtained asfollows: g Mass ofC = 2 mot X 12.01 mot = 24.02 g g Mass ofH = 6 mot X 1.008 mot = 6.048 g g Mass of 0 = 1 mot X 16.00 mot = 16.00g Mass of1mol C 2 H s OH = 46.07 g The mass percent (often called the weight percent) ofcarbon inethanol canbecomputed by comparing the mass of carbon in 1mole of ethanol to the total mass of 1mole of ethanol and multiplying theresult by 100: massofCin1mol C 2 H s OH Mass percent ofC = X 100% mass of1mol C 2 H s OH 24.02 g ---=- X 100% = 52.14% 46.07 g The mass percents ofhydrogen and oxygen inethanol areobtained inasimilar manner: mass ofHin1mol C 2 H s OH Mass percent ofH = f X 100% mass 0 1mol C 2 H s OH 6.048 g --~ X 100% = 13.13% 46.07 g mass of 0 in1mol C 2 H s OH Mass percent of 0 = X 100% mass of1mol C 2 H s OH 16.00g . ---=- X 100% = 34.73% 46.07 g Reality
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Unformatted text preview: Notice that the percentages add up to 100.00%; this provides a check that the calculations are correct. EXAMPLE 3.9 Carvone is a substance that occurs in two forms having different arrangements of the atoms but the same molecular formula (C lO H I4 0) and mass. One type of carvone gives caraway seeds their characteristic smell, and the other type is responsible for the smell of spearmint oil. Compute the mass percent of each element in carvone. Solution Where are we going? • To find the mass percent of each element in carvone What do we know? ./ Molecular formula, C lO H 14 What information do we need to find the mass percent? ./ Mass of each element (we'll use 1 mol carvone) ./ Molar mass of carvone...
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